Heretofore, porous substrates such as, for example, gypsum, cements, ceramics, bricks, porcelains, and natural stones have been used for various industrial applications. Especially, gypsum has been utilized in a wide range of fields for applications to engineering product models, dental models, dental embedded materials, arts, medical casts, tunnel reinforcements, construction boards, and so forth. Furthermore, recently, gypsum has been utilized in a laminated material of a 3D printer and hence attracted attention as an engineering material.
On the other hand, gypsum has such a disadvantage that the surface is relatively brittle. To compensate for this disadvantage, it is necessary to apply various coating agents to reinforce the gypsum surface. Particularly, an engineering product model, a dental model, and the like created using a 3D printer are demanded to have no missing part and scratch on the surfaces, and have high dimensional precisions in the modeling. In other words, the coating agents are demanded to be applied thinly for higher precisions of the models and to have sufficient hardness and strength at the same time.
As one of such coating agents, proposed is a composition containing a cyanoacrylate compound as a curable component diluted with a solvent having appropriate properties (hereinafter also referred to as cyanoacrylate composition) (Patent Literature 1). The cyanoacrylate compound imparts sufficient hardness and strength to the cured product when used for the aforementioned surface reinforcement. Moreover, since the cyanoacrylate compound reacts with moisture in air and is curable at normal temperature alone, it is easy to handle and the utilization thereof is promising.
However, in a state where an applied surface such as a coating is exposed to the atmosphere, the cyanoacrylate compound volatilizes and dissipates in air and undergoes a polymerization reaction with a small amount of water in air. The resulting fine solid particles adhere again to the coated product, causing a problem of a whitening phenomenon. As another adverse influence in this state, there is a problem of slow curing because the surface in contact with the atmosphere is cured little by little just with water in air on the surface. Further, in a case where gypsum is used as a porous substrate, when the cyanoacrylate compound is brought into contact with gypsum, the reaction therebetween is promoted because gypsum is a basic substance. Hence, in order to suppress the reaction, a suppressor such as a polymerization inhibitor needs to be added. However, as a trade off, the curability deteriorates, making it difficult to form a uniform coating film. Efforts have been made to solve these problems by using a cyanoacrylate composition made to be curable with an active energy ray such that the cyanoacrylate composition is cured quickly as appropriate by irradiating the applied surface with an active energy ray (Patent Literature 2).
However, when both of the above-described techniques are used in coating the porous substrate surface, the viscosity needs to be reduced to enhance the permeability. To accomplish this, the dilution with a certain amount of a solvent is required. As a result, the concentration of the cyanoacrylate compound in the system becomes too low, making it impossible to form a firm coating film. Further, the latter technique increases the size of the apparatus and the number of steps for the irradiation with an active energy ray. Hence, the achievement by a simpler method is desired.